The present invention relates to a method in conjunction with updating of one or more HLR-databases which are included in a GSM-type mobile telephone system, wherein updating of such a database is requested by transmitting to a number of VLR-databases a special signal which identifies the HLR-database concerned.
A GSM-network includes two types of net databases, HLR (Home Location Register) and VLR (Visitor Location Register). A network will normally include several HLRs and several VLRs. An example of a GSM network is illustrated in FIG. 3.
Among other things, each HLR-database has stored therein all permanent data for those subscribers, i.e. those mobile stations, which belong to this particular HLR. The telephone number of the mobile stations and information concerning additional services which are included in the subscription are examples of such data. The active status of the additional services and information which discloses in which VLR-database a respective mobile station is registered at that particular moment are also stored in HLR. The permanent data stored in HLR is secured by also storing the data in an external medium with the aid of "backup".
Among other things, there is stored in each VLR-database information which discloses the whereabouts of respective mobile stations that are registered in a particular VLR at that particular time. Each VLR also contains a copy of the subset of all subscriber data that is contained in HLR and is relevant to this VLR. This subset is obtained from HLR in conjunction with a new mobile station entering the area covered by a VLR, whereupon data is signalled from HLR to VLR with the aid of CCITT 7-signalling.
The described structure is highly vulnerable to errors and faults in the network, caused for instance by restarts in HLR or VLR and also by signalling associated errors. Consequently, there have been defined within GSM standardized work procedures for restoring data in these so-called node types in the most robust way possible, so as to avoid an error spreading to several nodes and resulting in breakdowns in the network.
When a VLR-database has lost its data for some reason or another, the VLR will update its data autonomously, by signalling backwards and forwards between itself and those mobile stations which are located within the area covered by this particular VLR. This means that those HLR-databases to which the mobile stations belong will not be affected immediately by a restart in a VLR. Data is collected from each individual HLR upon the next radio contact with a mobile station which belongs to this HLR.
On the other hand, if an HLR has been restarted, which means that the data therein may be corrupted, it is necessary for this HLR to request the assistance of different VLR in recreating parts of the data that was stored in HLR. This primarily concerns information as to which VLR mobile stations are registered at that time. According to GSM-standards, this is carried out by the HLR-database concerned informing all VLR-databases that this particular HLR has been restarted and needs to be updated with new data. This is effected with the aid of a "Reset" operation, which is signalled over the CCITT 7-network.
According to GSM-standards, when a "Reset-message" is received, those mobile stations which are registered in this VLR and which, at the same time, belong to the HLR-which needs to be updated are marked in each VLR-database in a special way. This marking is effected by allocating a flag, referred to as a "HLR confirmation flag" to each such mobile station. The intention with this procedure is to update HLR with data from VLR on the next occasion on which VLR has radio contact with a mobile station that has been marked with this flag. In this way, HLR receives information which discloses in which VLR respective mobile stations are registered at that particular time. Certain other data is updated at the same time, although this data is less important than the data which discloses to which VLR the mobile stations belong. It can also be mentioned that when updating HLR, a certain amount of data is transmitted from HLR to VLR, for instance subscriber data which applies to the mobile station.
Known methods for updating VLR-databases and HLR-databases are described in: ETSI TC GSM, Recommendation GSM 03.07, Restoration Procedures, Version: 3.2.0, Date: October 1990.
The known method of updating an HLR-database, however, is difficult to apply in practice, since a Reset-message does not contain information which discloses those mobile stations which belong to the HLR to be updated nor yet those VLR-databases which contain any data whatsoever required for the relevant updating procedure. Consequently, it is necessary to derive such information from the VLR-databases, by searching each and every one of said VLR-databases for the information obtained in conjunction with the entry of different mobile stations into the area covered by this VLR. Accordingly, it is necessary for each individual VLR to search through the whole of its subscriber register in order to find the HLR to which respective mobile stations belong. This search results in process capacity losses on the part of the VLR-databases, and these losses will, of course, be much greater on those occasions when a HLR is restarted several times within a short period of time or when several HLRs are restarted shortly after one another and several Reset-messages are therefore transmitted in sequence. Each VLR will therewith search through its subscriber register for each Reset-message received.